A light gas gun is a projectile launcher employing a gas having a low atomic number, usually hydrogen or helium. One limiting factor on the speed of a projectile coming from a gun is the speed of sound in the working fluid. This is because the pressure waves created by the propulsive force are essentially unable to propagate speeds higher than the speed of sound within a given medium. Thus, light gases are particularly advantageous for accelerating a projectile at very high velocities because the speed of sound in a gas is a function of the inverse square root of the molecular weight. The speed of sound also increases with the temperature of the fluid so that heat formed by the compression of the light gas also serves to increase the maximum possible speed.
In a typical application, the light gas is pressurized and/or heated in a chamber having a rupture disk located at one end. In some examples, this is done by using a large diameter piston, powered by an explosive chemical reaction, to force a gaseous working fluid through a smaller diameter chamber containing the projectile to be accelerated. The rupture disk is situated behind a projectile located within a barrel. In response to the increased pressure and/or heat, the light gas ruptures the carefully calibrated rupture disk and then is brought at very high velocity against the rear of the projectile, thereby accelerating the projectile from a breech of a barrel through the barrel muzzle.
Some designs employ a multi-stage piston, wherein by using multiple pistons in series, each piston residing in a chamber with successively smaller cross-sectional area, the final piston is accelerated to compress the light gas very quickly into an area that is at or near the cross-sectional area of the projectile and/or sabot. See, e.g., U.S. Pat. No. 3,311,020; and U.S. Pat. No. 4,658,699.
One limitation of present designs is the use of explosives, which is the exclusive source of propulsive force in the prior art designs. Light gas guns are often used in jurisdictions where the use of such explosive charges requires a permit. Because a light gas gun may be used only occasionally in a single location, the process of procuring a permit is a significant issue. Also, the use of such explosive charges creates obvious safety issues. See, e.g., U.S. Pat. No. 4,038,903; U.S. Pat. No. 5,194,690; and U.S. Pat. No. 5,429,030.
Another limitation of prior art designs is the need for precise manufacturing of rupture disks. The rupture disk is essentially the triggering mechanism by allowing the light gas gun to fire when the rupture disk fails. Current designs require rupture disks to be manufactured to very precise specifications in order to achieve predictable performance. This increases the cost of operating a light gas gun while presenting some questions regarding the ability to tailor the performance to a specific application. See, e.g., U.S. Pat. No. 5,762,057.
Thus, there remains a need in the art for a light gas gun apparatus and associated method that is versatile yet predictable, and which may operate without the use of explosive charges.